Compact scanning optical system

ABSTRACT

The disclosure of the current invention describes a compact optical system for and method of forming an image on an intermediate image-forming surface such as a photoreceptor drum at a high speed. An image-forming light source such as a laser light source is placed between an image-focusing element such as a focusing mirror and an image-scanning unit such as a polygon mirror. According to one preferred embodiment, the image-forming light source is placed in a scanning area defined by a predetermined scanning angle of the image scanning unit.

FIELD OF THE INVENTION

The current invention is generally related to a method of and a systemfor providing a compact optical system and more particularly related toa method of arranging scanning optical components in a compact space anda compact optical system having a light source located between animage-reflecting surface such as a polygon mirror and an image-focusingelement such as a focusing mirror.

BACKGROUND OF THE INVENTION

An optical system is used in image duplication devices such as facsimilemachines, copiers and printers. In general, the optical system is housedin a single housing unit and is located near an intermediateimage-forming surface such as a photoreceptor drum. The optical systemincludes an image-forming light source, an image-reflecting surface andan image-focusing element to form a desired image on the intermediateimage-forming surface by repeatedly scanning the image-forming light ina predetermined direction. To accomplish an efficient scanning, theimage-reflecting surface has multiple reflecting surfaces and is rotatedat a high speed. The light source is located at a certain distance fromthe rotatable reflecting surface at a predetermined angle so that adesired scanning angle is obtained. For these and other reasons, theabove described prior art optical housing unit generally takes a certainamount of space.

In the efforts to manufacture compact duplication devices, the abovedescribed optical system or housing unit needs to be reduced in size.Referring to FIG. 1, one prior art attempt in reducing the overall sizeof the optical housing unit includes Japanese Patent 5-19196 whichdiscloses an optical housing unit 50 whose mounting portions 51A, 51Band 51C are located inside the optical housing unit 50. Thus, spaceoccupied by otherwise protruding mounting portions 51A-51C is saved, andthe overall housing unit size is reduced.

Still referring to FIG. 1, Japanese Patent 5-19196 further discloses alight source 1 located adjacent to a rotatable image-reflecting surface8 so as to reduce the overall size of the housing unit 50. The lightsource 1 emits an image-forming light towards the rotatingimage-reflecting surface 8 which scans the light within a predeterminedscanning angle through an image-focusing lens 4. The scanned light isthus focused on a predetermined intermediate image-forming surface by afocusing lens 4 to form a desirable image thereon. However, a certainpredetermined distance must be provided between the reflecting surface 8and the image focusing element 4. Additionally, the relative position ofthe light source 1 is inflexible with respect to the position of therotatable reflecting surface 8. In other words, the light source 1 mustbe placed outside of the scanning angle of the rotatable reflectingsurface 8, and a relatively large angle of incidence of the incominglight on the reflecting surface 8 also must be maintained. Consequently,the reflecting surface area needs to be relatively large. For thesereasons, the overall housing unit size is not substantially reduced.

Referring to FIG. 2, another prior art effort as disclosed in JapanesePatent 6-148541 employs an additional reflecting surface 60 between alight source 1 and a rotatable reflecting surface 8 for modifying anangle of the originally emitted light by the light source 1. The use ofthe angle modifying reflecting surface 60 allows the positionalarrangement of the light source 1 and the rotatable reflecting surface 8to be more flexible. However, the above described large angle ofincidence as well as a large reflecting surface area on the rotatablereflecting surface must be still provided to form a desirable image.

In view of the above prior art, a flexible compact optical system isdesired for various duplication devices of a further reduced size.

SUMMARY OF THE INVENTION

In order to solve the above described and other problems, according toone aspect of the current invention, one method of projectingimage-forming light onto a temporary image-forming surface via arotatable image-reflecting surface and an image-focusing element,includes the following steps of: a) placing an image-forming lightsource in an area defined by a predetermined scanning angle of therotatable image-reflecting surface and located between the rotatableimage-reflecting surface and an image-focusing element; b) projectingthe image-forming light towards the rotatable image-reflecting surface;c) scanning the image-forming light towards the image-focusing elementwhile rotating the rotatable image-reflecting surface; and d) focusingthe image-forming light reflected by the rotatable image-reflectingsurface onto the temporary image-forming surface.

According to a second aspect of the current invention, a method ofprojecting image-forming light onto a temporary image-forming surfacevia a rotatable image-reflecting surface and an image-focusing element,the image-focusing element having a reflector portion for reflecting theimage-forming light, includes the following steps of: a) placing animage-forming light source in an area defined by an extent of therotatable image-reflecting surface and an image-focusing element; b)projecting the image-forming light towards the reflector portion whichreflects the image-forming light towards the rotatable image-reflectingsurface; c) scanning the image-forming light towards the image-focusingelement while rotating the rotatable image-reflecting surface; and d)focusing the image-forming light reflected by the rotatableimage-reflecting surface onto the temporary image-forming surface.

According to a third aspect of the current invention, a system forprojecting image-forming light onto a temporary image-forming surface,includes: an image-focusing element for focusing the image-forming lightonto the temporary image-forming surface; a rotatable image-reflectingsurface located near the image-focusing element for reflecting theimage-forming light and for scanning the image-forming light within apredetermined scanning angle towards the image-focusing element whilerotating the rotatable image-reflecting surface; and an image-forminglight source located in an area defined by the predetermined scanningangle and an extent of the rotatable image-reflecting surface and theimage-focusing element for projecting the image-forming light towardsthe rotatable image-reflecting surface.

According to a fourth aspect of the current invention, a compact opticalsystem for projecting image-forming light onto a photoreceptive drumsurface, includes: a fθ mirror having a curved reflective surface forfocusing the image-forming light so as to form an image on thephotoreceptive drum surface, the image-focusing element also having anintegral reflector portion for reflecting the image-forming light; arotatable polygon mirror located near the fθ mirror for reflecting theimage-forming light towards the fθ mirror and for scanning theimage-forming light towards the fθ mirror while the polygon mirror isbeing rotated; and an image-forming light source located in an areadefined by an extent of the rotatable polygon mirror and the fθ mirrorfor projecting the image-forming light towards the reflector portionwhich reflects the image-forming light towards the polygon mirror.

According to a fifth aspect of the current invention, a single componentboard used in a compact optical system, includes: a rotatableimage-reflecting surface located on the single component board forreflecting an image-forming light so as to scan the image-forming lightwithin a predetermined scanning angle while rotating the rotatableimage-reflecting surface; and an image-forming light source located onthe single component board in an area defined by the predeterminedscanning angle for projecting the image-forming light in a predetermineddirection with respect to the rotatable image-reflecting surface.

According to a fifth aspect of the current invention, an image-focusingelement used in a compact optical system, includes: an image-focusingsurface for forming an image on a predetermined surface in response toan incoming image-forming light; and a reflector portion located on theimage-focusing surface for directly reflecting the incomingimage-forming light in a predetermined direction.

These and various other advantages and features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed hereto and forming a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to the accompanying descriptive matter, inwhich there is illustrated and described a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates a top view of a prior art opticalsystem.

FIG. 2 diagrammatically illustrates a top view of another prior artoptical system.

FIG. 3 illustrates a perspective view of one preferred embodiment of thecompact optical system according to the current invention.

FIG. 4 illustrates a cross-sectional view of the preferred embodiment ofthe compact optical system as taken at a plane indicated by a line A--Aof FIG. 3.

FIG. 5 illustrates a perspective view of detailed disassembledcomponents of an image-forming light source used in a compact opticalsystem according to the current invention.

FIG. 6A illustrates a perspective view of another preferred embodimentof the compact optical system according to the current invention.

FIG. 6B illustrates an enlarged cross-sectional view of a mirror and animage-focusing element as taken at a line B--B of FIG. 6A.

FIG. 7 illustrates a cross-sectional view of the preferred embodiment ofthe compact optical system as taken at a plane indicated by a line B--Bof FIG. 6.

FIG. 8 illustrates a perspective view of yet another embodiment of thecompact optical system according to the current invention.

FIG. 9 diagrammatically illustrates a relationship between a first areadefined by a predetermined scanning angle of a rotating reflectingsurface and a second area defined by the rotating reflecting surface andan image-focusing element.

FIGS. 10A and 10B each illustrates a preferred embodiment in across-sectional view taken at a line C--C of a detection unit as shownin FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to the drawings, wherein like reference numerals designatecorresponding structure throughout the views, and referring inparticular to FIG. 3, a prospective view of one preferred embodiment ofthe compact optical system according to the current invention isillustrated. An image-forming light source 1 such as a laser lightsource and a rotatable image-reflecting surface 8 such as a polygonmirror are mounted on a single component board 10. The light source 1 ishoused in a light source housing 14 and emits light towards therotatable image-reflecting surface 8. The emitted light reaches therotatable surface 8 which is continuously rotated at a high speed by adriving unit 7. The rotating surface 8 thus scans the light in ahorizontal direction within a predetermined scanning angle towards animage-focusing element 4. The light source 1 is located on the componentboard 10 between the rotatable reflecting surface 8 and theimage-focusing element 4. The light source 1 is also located within anarea defined by the predetermined scanning angle of the rotatablereflecting surface 8. The predetermined scanning angle is defined to bea relative angular range of the rotatable reflecting surface 8 about itsrotational axis for covering a predetermined horizontal scan distance onthe intermediate image-forming surface. According to a second embodimentof the current invention, the light source is located on a lineconnecting the image-focusing element 4 and the rotatable reflectingsurface 8.

Still referring to FIG. 3, an image focusing system includes the firstimage-focusing element 4 and a second image-focusing element 21 to forma focused image on an intermediate image-forming surface 15. The firstimage-focusing element 4 in the preferred embodiment is also termed as afθ mirror, and the body is made of plastic while the surface is coatedwith aluminum. A surface 16 of the fθ mirror 4 has a predeterminedcurvature in both a scanning as well as a sub-scanning direction toserve as a light condenser. The scanning direction is a horizontaldirection as indicated by a line 17 on the fθ mirror 4 while thesub-scanning direction is perpendicular to the scanning direction. Thelight condensing surface 16 thus reflects the scanned light towards thetemporary image forming surface 15. The second image-focusing element 21is located on the light path between the fθ mirror 4 and theintermediate image-forming surface 15. According to one preferredembodiment, the second image-focusing element 21 is a longsemi-cylindrical lens having a predetermined curvature in thesub-scanning direction for correcting a distortion of an image in thesub-scanning direction which is caused by the rotatable image-reflectingsurface 8.

In order to form a desirable image on the intermediate image-formingsurface 15, a light is repeatedly scanned in the scanning directionwhile the rotatable image-reflecting surface 8 is being rotated. Foreach scanning cycle, a detection unit 5 also located on the componentboard 10 detects an onset of the horizontal sweep. As the rotatablereflecting surface 8 is rotated to a certain angle so that the scannedlight reaches near one end of the first image-focusing element 4, thereflected light is detected by a photo-sensitive element in thedetection unit 5. According to one preferred embodiment of the currentinvention, the single component 10 additionally includes an onsetdetection signal generation circuit 22 for generating a scan onsetsignal, a cable 23 for connecting the component board 10 to a controlunit by sending and receiving signals such as the scan onset signal, andother components such as a light source control circuit for adjustingthe intensity of the light source.

Now referring to FIG. 4, a cross sectional view of the above describedpreferred embodiment shows elements in a compact optical housing unit 6.The housing unit 6 houses the single component board 10, the componentslocated on the component board 10 as described in reference to FIG. 3,the first image-focusing element 4 and the second image-focusing element21. The component board 10 is mounted inside the housing unit 6 at boardmounting portions 6a, 6b and 6c. As described above, the singlecomponent board 10 includes the light source 1 and the rotatablereflecting surface 8. The rotatable reflecting surface 8 is mounted on adrive shaft 7a of a motor 7. According to one preferred embodiment, thereflecting surface 8 is mounted on the drive shaft 7a, and thereflecting surface 8 is provided by cutting two surfaces parallel to itsdiameter. Further, the drive shaft housing 9 is fit in the singlecomponent board 10.

Referring to both FIGS. 4 and 5, some detailed sub-components of thelight source 1 are respectively illustrated in a cross-sectional andprospective view. A laser generating unit 11 generates laser light inresponse to a laser control unit 23, and a collimator lens 12 on aholder 26 collimates the generated laser light in substantially parallelrays of light. An aperture 13 of a predetermined size is formed on afront panel 27 and allows the passage of the light in a desireddiameter. The above described sub-components of the light source 1 ishoused in a light source housing 14a through 14e, and the housingattachment portions 14d of the light source housing 14 are mounted atthe through holes 10a of the single board component 10. The front panel27 is sandwiched between the light source housing 14 and the componentboard 10. The component board is in turn mounted on the housing boardholding portions 6b and 6c, and the board is further screwed onto thehousing by screws 28.

Referring back to FIG. 4, light travels from the light source 1 to thesecond focusing element 21 in a zigzag fashion. The first image-focusingelement 4 is located near one side of the compact optical housing unit 6while the second image-focusing element 21 is located near the other endof the housing 6 above the component board 10. The laser light from thelight source 1 is emitted directly towards the rotatable reflectingsurface 8 at a first predetermined vertical angle with respect to thecomponent board 10. The reflecting surface 8 then reflects the lighttowards the image-condensing surface 16 of the first focusing element 4.The condensed light then travels toward the second image-focusingelement 21 at a second predetermined vertical angle with respect to thecomponent board 10. Because of the above light projection angles, thelight is not interfered in its light path towards the intermediateimage-forming surface during the image formation process. Furthermore,the image formation is accomplished by using less space due to the abovedescribed topology of the components.

Now referring to FIG. 6, a prospective of the third embodiment of thecompact optical system according to the current invention isillustrated. Since many components in the third embodiment aresubstantially similar to those described in reference to the abovepreferred embodiments, the description for these similar components arenot reiterated here but incorporated herein by reference. The thirdpreferred embodiment differs in the position of the light source 1 and afirst image-focusing element 4'. Although the light source 1 is locatedon the single component board 10, the light source 1 emits light towardsthe first image-focusing element 4' which is located at a substantiallysame position with the above described first and second embodiments. Inother words, the light source in the third embodiment is positioned toapproximately 180° from that of the first and second embodiments. Moreprecisely speaking, the light is emitted towards a reflector portion 2of the first image-focusing element 4'. The reflected light reaches therotatable reflecting surface 8 for scanning the light in a scanningdirection as already described above. The scanned light then reaches thelight condensing surface 16' of the first image-focusing element 4'. Thecondensed light travels towards an intermediate image-forming surface 15through a second image-focusing element 21 to form a desirable image onthe image-forming surface 15.

Still referring to FIG. 6A, according to one preferred embodiment, thereflector portion is located near the center of the image-focusingsurface 16' and integrally formed on the surface 16'. To project thelight to the reflector portion 2, the light source 1 is on a lineconnecting the center of the image-focusing element 4' and the rotatablereflecting surface 8. However, according to another embodiment, thereflector 2 is located slightly off the center of the image-focusingelement 4', and accordingly, the light source 1 is located on thecomponent board 10 between the rotatable reflecting surface 8 and theimage-focusing element 4'. The position of the light source 1 isprimarily determined by the position of the reflector portion 2 withrespect to the image-focusing surface 16. Since the reflector locatednear the center of the image-focusing surface 16, an angle of incidenceof the incoming light onto the rotatable image-reflecting surface isoptimally minimized. Consequently, the size of the rotatable reflectingsurface is also desirably minimized for a compact optical system.Furthermore, since the reflector 2 is integrally formed with thefirst-image focusing element 4', the reflector 2 neither requiresadditional space nor a complicated assembly process.

Now referring to FIG. 7, a cross-sectional view of the above describedthird embodiment of the compact optical system according to the currentinvention is illustrated. The description of the elements in the compacthousing unit 6 are substantially the same as that for the first andsecond embodiments except for the reflector portion 2 and the additionallight path associated with the reflector portion 2. As already describedabove, the light source 1 is positioned to emit light towards thereflector portion 2. The reflector portion 2 reflects the emitted lighttowards the rotatable reflecting surface 8. According to one preferredembodiment, the reflector 2 has a substantially flat surface as shown insolid line in FIG. 6B. According to another embodiment, the reflector 2has a substantially curved surface as indicated in a dotted line also inFIG. 6B. Since the curved reflector 2 substantially eliminates adistortion of an image in the sub-scanning direction which is caused bythe rotatable image-reflecting surface 8, the second image-focusingelement 21 is not necessary in the compact optical system employing thecurved reflector 2.

Referring to FIG. 8, the fourth embodiment of the compact optical systemaccording to the current invention is illustrated in a perspective view.The components of the fourth embodiment are substantially similar to theabove described third preferred embodiment. However, in the fourthpreferred embodiment, the light source is located in an area defined bythe extent of the first image-focusing element 4 and the rotatablereflecting surface 25. In other words, one dimension of the above areais defined by a first distance between the first image-focusing element4 and the rotatable reflecting surface 25, and the other dimension ofthe same defined area is the width of the first image-focusing elementor the scanning distance at the first image-focusing element 4.

In order to visually specify the above defined rectangular area, brieflyreferring to FIG. 9, a predetermined angle of the rotatable reflectingsurface 8 is designated by α, and a rectangular area β indicates theabove defined rectangular area. In general, the rectangular area βincludes the scanning area α and is generally larger than the scanningarea α.

Referring back to FIG. 8, to accommodate the placement of the lightsource 1 in the vicinity of one corner in the above defined rectangulararea β, a reflector portion 2 is placed near one end of theimage-focusing element 4 at a predetermined angle to reflect the lighttowards the rotatable reflecting surface 25. The reflected light is thenscanned by the rotatable reflecting surface 25 to form a desirableimage. The reflecting surface 25 includes four individual surfaces, andeach surface has the same predetermined scanning angle. As describedabove, the placement or topology the components in the compact opticalsystem according to the current invention is flexible withoutsacrificing the optimally minimal size of certain components.

Now referring to FIGS. 10A and 10B, a cross-sectional view of twoembodiments of a detection unit 5 is shown. The detection unit 5 islocated on a component board 10 and determines the onset of eachscanning cycle by detecting light reflected by a peripheral portion ofthe image-focusing element 4. Referring to FIG. 10A, one embodiment ofthe detection unit 5 includes a roof mirror 19a angularly located insidethe slant portion 19 to guide the light towards a photo sensor 18. Theroof mirror is made of a layer of aluminum coated on the inside wall 19.FIG. 10B shows another embodiment of the photo detection unit 5 whichadditionally includes a cylindrical lens 20a placed before the mirror20b. The lens 20a is placed to accurately guide the light towards themirror 20b and to the photo sensor 18 in case the light path is affectedby a less-than perfect image-focusing element.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size and arrangement of parts, as well as implementation in software,hardware, or a combination of both within the principles of theinvention to the full extent indicated by the broad general meaning ofthe terms in which the appended claims are expressed.

What is claimed is:
 1. A method of projecting image-forming light onto a temporary image-forming surface via a rotatable image-reflecting surface and an image-focusing element, comprising the following steps of:placing an image-forming light source in an area defined by an extent of the rotatable image-reflecting surface and an image-focusing element; placing a flat reflector portion on the image-focusing element; projecting the image-forming light towards the flat reflector portion which reflects the image-forming light towards the rotatable image-reflecting surface; scanning the image-forming light towards the image-focusing element while rotating the rotatable image-reflecting surface; and focusing the image-forming light reflected by the rotatable image-reflecting surface onto the temporary image-forming surface.
 2. The method of projecting image-forming light onto a temporary image-forming surface according to claim 1 wherein in said placing step, said area is defined by a predetermined scanning angle about a rotational center of the rotatable image-reflecting surface.
 3. The method of projecting image-forming light onto a temporary image-forming surface according to claim 2 wherein the image-forming light source is placed on a line between the rotational center of the rotatable image-reflecting surface and a center of the image-focusing element where the reflector portion is located.
 4. The method of projecting image-forming light onto a temporary image-forming surface according to claim 3 wherein the reflector portion and the rotatable image-reflecting surface reflect the image-forming light at a respective predetermined angle in a vertical direction so as to prevent the reflected image-forming light from interfering with each other.
 5. The method of projecting image-forming light onto a temporary image-forming surface according to claim 1 wherein in said placing step, the image-forming light source is placed outside a second area defined by a predetermined scanning angle about a rotational center of the rotatable image-reflecting surface.
 6. The method of projecting image-forming light onto a temporary image-forming surface according to claim 5 wherein in said projecting step, the reflector portion is located near one end of the image-focusing element.
 7. The method of projecting image-forming light onto a temporary image-forming surface according to claim 1 wherein said scanning step is repeated for horizontal sweeps and for each sweep said scanning step further comprises a step of detecting a beginning of each sweep of said scanning.
 8. A compact optical system for projecting image-forming light onto a photoreceptive drum surface, comprising:a fθ mirror having a curved reflective surface for focusing the image-forming light so as to form an image on the photoreceptive drum surface, the image-focusing element also having an integral flat reflector portion for reflecting the image-forming light; a rotatable polygon mirror located near said fθ mirror for reflecting the image-forming light towards said fθ mirror and for scanning the image-forming light towards said fθ mirror while said polygon mirror is being rotated; and an image-forming light source located in an area defined by an extent of said rotatable polygon mirror and said fθ mirror for emitting the image-forming light towards said flat reflector portion which reflects the image-forming light towards said polygon mirror.
 9. The compact optical system for projecting image-forming light onto a photoreceptor drum surface according to claim 8 wherein said image-forming light source is placed in said area defined by a predetermined scanning angle about a rotational center of said polygon mirror.
 10. The compact optical system for projecting image-forming light onto a photoreceptor drum surface according to claim 8 wherein said image-forming light source is placed on a line between the rotational center of said polygon mirror and a center of said scanning angle of said fθ mirror where said flat reflector portion is located.
 11. The compact optical system for projecting image-forming light onto a photoreceptor drum surface according to claim 10 wherein said flat reflector portion and said polygon mirror reflect the image-forming light at a respective predetermined angle in a vertical direction so as to prevent the reflected image-forming light from interfering with each other.
 12. The compact optical system for projecting image-forming light onto a photoreceptor drum surface according to claim 8 wherein said image-forming light source is placed outside a second area defined by a predetermined scanning angle about a rotational center of said polygon mirror.
 13. The compact optical system for projecting image-forming light onto a photoreceptor drum surface according to claim 12 wherein said fθ mirror has two horizontal ends, said flat reflector portion being located near one of said horizontal ends of said fθ mirror.
 14. The compact optical system for projecting image-forming light onto a photoreceptor drum surface according to claim 12 wherein said polygon mirror repeatedly scans the image-forming light in a predetermined horizontal direction.
 15. The compact optical system for projecting image-forming light onto a photoreceptor drum surface according to claim 14 further comprising a scan onset detection unit located near said fθ mirror, as said polygon mirror initiates a scan, said scan onset detection unit detecting a beginning of the scan of the image-forming light onto the photoreceptor drum surface. 